1. Field of the Invention
Aspects of the present invention relate to an image forming apparatus and an image forming method thereof.
2. Description of the Related Art
An image forming apparatus forms an image on a recording medium, according to a printing signal from a host device. In general, an image forming apparatus includes: a paper feeding part, which stacks pages of the recording medium; an image forming part, which forms an image on the recording medium from the paper feeding part; and a paper discharging part, which discharges the recording medium having the image formed thereon. An image forming apparatus can be classified as a mono-type, where images are printed in grayscale on a recording medium, and a color-type, where images are printed in color on a recording medium. Color images can be formed by a combination of four colors, such as, yellow, magenta, cyan, and black.
FIG. 1 schematically illustrates a configuration of a conventional color-type image forming apparatus 10. The image forming apparatus 10 includes: a paper feeding part (not shown), which stacks pages of a recording medium; developing devices 30Y, 30M, 30C, and 30K, which apply different developing agents to the recording medium; and a transport belt 23, which sequentially transfers the recording medium to the developing devices 30Y, 30M, 30C and 30K.
In an image forming method using the image forming apparatus 10, a printing signal is received from a host device. The recording medium is picked up from the paper feeding part and is brought into contact with a photosensitive body 31 of each developing device 30, while being transferred by the transport belt 23. Transfer rollers 25Y, 25M, 25C, and 25K, respectively corresponding to the developing devices 30Y, 30M, 30C and 30K, are disposed at a rear side of the transport belt 23 and assist in the transfer of developing agents from the photosensitive bodies 31 to the recording medium. In this way an image is formed. At least two different developing agents overlap to form a color image.
The conventional image forming apparatus 10 drives the developing devices 30Y, 30M, 30C, and 30K, in response to the printing signal (print job) from the host device. Even if images to printed are made of only one color applied by a specific developing device, all of the developing devices 30 are driven. The photosensitive bodies 31, of the specific developing devices 30 corresponding to one or more colors of the image data, apply a developing agent while being in contact with the recording medium, but the other developing devices operate without applying a developing agent.
The developing agent functions as a lubricant, to prevent components in the developing devices from being worn when they are driven. If the components are driven without the flowing of the developing agent, they are worn by contact and friction. For example, if the photosensitive body is in contact with the recording medium without applying the developing agent, it may be scratched on its surface. If image data corresponding to a developing device of a specific color, is applied in large quantities, e.g., a hundred pages at a time, the components of the other developing devices of different colors may be prematurely worn out.
If the components of an infrequently used developing device are worn out, the developing device may not function properly even if it retains a supply of a developing agent. That is, a developing device of a color which is not frequently used has a decreased life span. In this case, a user should replace the developing device, even though it retains a supply of developing agent, resulting in waste.